Is the expected image quality (scaled to the airmass of your target) sufficient for your program? What is the minimum image quality necessary for the science?

What level of cloud cover is acceptable? Is photometric weather required?

Water vapor content is usually only relevant if you are observing in the thermal IR (3 to 5 microns).

Sky background in the near-IR doesn't vary greatly, but it does depend on water vapor at 3 to 5 microns.

Note the product of the probabilities of each of the conditions listed above. This is related to the likelihood of your observations being executed, especially in the lower ranking bands. You might wish to reconsider some of your constraints if the product is very low.